Fracture bridging in oil wells



NOV- 18, 1958 w. H. Ril-:GER

FRACTURE BRIDGING IN OIL WELLS Y Filed Feb. l5, 1957 m. k .W m.

Embruns aumento 1N orL WELLS William H. Rieger, Indianapolis, Ind., assignor to Reilly Tar & Chemical Corporation, Indianapolis, Ind., a corporationl of Indiana Application February 15, 1.957, Serial No. 640,418

- 2 Claims. (Cl. 166-.22)

This invention involves a discover-y of a` composition for bridging a fracture orfractures in a so-called multiple fracturing process employed to increasethe productivity of an oil well and also a gas well. t

Reference is` made to a co-pending application for patent by Merritt M. Otto, Serial No. 565,780; assigned tothe assigneeof thepresen-t application, and still pending.

It is a frequent occurrence inthe oil fields that when an oil well is new, but most: usually after-a. period of flow from the well, it. fails to producethe quantity of oil which the well should be capable of`producing because of a particuar formation of theearth about the lower end of the well, which. formationV is inthe oil4 bearingstratum, and more particularly which. formation is not permeable to that degree which will permit a rapid ow of the oil into the well.

Obviously if this oil 'beating stratum can be made more permeable, that is, broken up into a large number of channels, such as fissures, or extended cracks into the stratum, the productivity of the well may be appreciably increased. With this thought in mind, there has heretofore been developed and now employed in commercial usage, a so-called multiple fracturing process for increasing the productivity of wells. In this practice, the oil bearing stratum is fractured in an isolated zone by injecting into the well a rather viscous liquid of the napalm gel type and subjecting the introduced fluid to a suicient pressure which will cause the fluid to actually rupture or fracture the stratum for some little distance laterally from the bore hole. Such pressure generally runs above three thousand pounds per square inch. The fracturing is indicated by a drop in the pressure, this pressure being created at the top of and externally of the well.

However a single fracture of the oil bearing stratum normally is not sufficient to obtain the lgreatest possible flow of the oil into the bore, and then the problem arises as to how to block olf the `original fracture in order to set up additional fracturing ofthe stratum either above or below that original fracturing. To accomplish this, an additive is added to the fracturing Huid for the express purpose of bridging over the initially formed fracture and withholding flow of the fluid into that fracture that is from the oil strata into the bore, until at least such a time as an additional fracture or fractures, have been produced in the stratum. In this manner, a multiple fracturing could be carried on at isolated zones in the Well bore. Once a multiple fracturing has been accomplished, or even an individual fracturing, the additive necessarily has to be removed from the fracture to permit the oil to flow through that fracture into the bore.

In the disclosure of the application above noted, the material hit upon to set up the bridging action to cause a fracture opening into the bore is granular naphthalene in various sizes of granules or particles. That material was selected because of its relatively low melting point of eig. ty degrees C. at atmospheric pressure, the melting nited States Patentn O point of course increasing` under the hydraulic pressure employed in setting up the fracturing.

Now the use of naphthalene as indicated inV that application is quite suitable as a bridging agent for multiple fracturing of oil wells having hole temperatures of from one hundred to one hundred twenty degreesF. However there are many wells which have a temperature lower thanl that, rangingaround` eighty to ninety degrees F. At that range of temperatures, the rateof solution ofAv the naphthalene in the crude oil is too low'for adequate removal.

`Also another difficulty with a naphthaleneyis that it cannot be satisfactorily stored at the one hundred twenty degree F. without caking. Temperatures of one hundred twenty degrees F. are frequently encountered particularly in the southern States 0fthe` U. S. and also'particularly where the material is stored in black painted or coated drums in the open and exposed to sunshine.

Thoserequirements of the rate` of solution' inA crude oil and: storage of a material without its becoming soft and tacky, or even melting, or becoming caked, up to ternperatures of one hundred twenty degrees F. present; quite a problem because, ingeneral, a material which has the correct solution rate at the temperature of eightydegrees F. isl accompanied by a low melting point which prevents the storage temperature of one hundredftwenty degrees F.

without changing its formi For example, mixtures of naphthalene` with` high-melting paratiin, withfvariousV waxes'andwith compoundssuch as ortho-phenylphenol or biphenyl behave in this manner. A few mixtures were discovered which passed both solubility and storage tests, but these mixtures were impractical because of either too high a cost or of low availability.

A single compound, biphenyl was discovered to have highly usable qualities for the purpose intended when it is compressed, crushed, sized, and coated lightly with an anti-caking agent such as one percent of a nely divided silica gel, the biphenyl thus treated being storable at one hundred twenty degrees F. for extended periods without caking or becoming tacky or soft. Also its rate of solubility in kerosene (equivalent to crude oil) at eighty degrees F. comparesvery favorably with the solubility of naphthalene in kerosene at one hundred degrees F.

Thus in discovering this material, biphenyl7 and treating it as indicated, it becomes a highly desirable bridging agent for this multiple fracturing process of oil wells wherein the hole temperatures come within the -90 degrees F. range.

A good bridging agent should be approximately ninety percent dissolved in from six to seven hours and not less in order that fracturing may be carried on at different zones in the bore while previously fractured zones are bridged. The solubility curves for naphthalene at eighty degrees and one hundred degrees F. and for biphenyl at eighty degrees F. are shown in the drawing forming a part of this application. The biphenyl crystal-like material is crushed and sized to have a range in sizes of individual particles to the end that large particles may initially enter the ssures or cracks of a fracture and then be surrounded by smaller particles .which will effectively block flow along -the fissures or cracks. The silica gel is of that sizing wherein the particles will be extremely minute. For example the silica is divided into particles of sub-microscopic sizes ranging from about 0.02 micron to about 5 microns. The extreme minuteness of the particle sizes of this silica gel is hard to visualize, since a c ubic inch of it will contain more than ve billion silica particles.

This silica gel which is employed to lightly coat the individual particles of the biphenyl is not at al1 soluble in the hydro-carbon oils, that is the crude oils in the well, and it is of such nature that it has an extremely strong ainity for the oils themselves, this atl'inity resulting in a gel which forms and is readily flowed out of the fractures or ssures by the flow of the crude oil so that there is no tendency whatsoever for the silica to lodge in the irregular pockets and wall formations of the fracture, the biphenyl itself being dissolved out of the fracture as readily and as completely as it would have been had the particles Cil not been coated with the silica gel. This coating of the 'y biphenyl particles with the silica gel may range from one percent to as much as tive percent by weight of the gel to the biphenyl Without in any way adversely aifecting the bridging Iaction and its resulting removal. The silica gel causes the biphenyl particles to be quite free owing under conditions up to the higher temperature of one' hun- Ydredrtwenty degrees s In order to employ the biphenyl treated as above indicated, this material is added to the fracturing fluid after l an initially formed fracture so that the fracturing iluid into that zone in any appreciable amount, that fracturing fluid being the vehicle which carries the biphenyl into the fracture. The additive once filling in the fracture, will withhold the fracturing'fluid so that its pressure will rupture the oil stratum material at a different zone, and

then when there are sucient fractures produced,4 the pressurizing uid is pumped out, and the crude oil itself dissolves out the additive material from the fractures. n

I claim:

1. That method of bridging a fractured yoil bearing j stratum in an oil well wherein there exists a temperature l at the stratum 'to be bridged'of approximately 80 to 90 degrees F., which method comprises dusting graduated particles of biphenyl with dry silica gel in particle sizesvgjr', ranging from approximately 0.02 micron to 5 microns in. the proportion of silica gely to biphenyl ranging from approximately one to five percent by weight; adding the mixture to a pumpable fracturing uid; pressurizing the fluid containing the additive at said stratum to fracture 1'5""the stratum; and V4allowing the Vsilica gel, through itsV ain- 'I ity with the crude oil, to be flowed out of the fracture. resulting from said pressurizing to expose the bridged biphenyl to solvent action of the oil.

2. An additive to a fracturing fluid employed in developing an oil Well at temperatures ranging approximately from 80 to` 90'degrees F., which consists of dry biphenyl in a range of particle sizes, kand an individual, particle -coating of silica gel in particle sizes rangingfrom approximately 0.02 to five microns, the ratio of the coatp ing to biphenyl being in the range of from one to ve percent by weight of silica gel. l v Y References Cited in the le of this patent v Y' UNITED STATES PATENTS Pine et al. Apr. 1, 1913 1,057,667 2,634,098 Armentrout Apr. 7, 1953 2,734,861 Scott et al. Feb. 14, 1956 

1. THAT METHOD OF BRIDGING A FRACTURED OIL BEARING STRATUM IN AN OIL WELL WHEREIN THERE EXISTS A TEMPERATURE AT THE STRATUM TO BE BRIDGED OF APPROXIMATELY 80 TO 90 DEGREES F., WHICH METHOD COMPRISING DUSTING GRADUATED PARTICLES OF BIPHENYL WITH DRY SILICA GEL IN PARTICLE SIZES RANGING FROM APPROXIMATELY 0.02 MICRON TO 5 MICRONS IN THE PROPORTION OF SILICA GEL TO BIPHENYL RANGING FROM APPROXIMATELY ONE TO FIVE PERCENT BY WEIGHT; ADDING THE MIXTURE TO A PUMPABLE FRACTURING FLUID; PRESSURIZING THE FLUID CONTAINING THE ADDITIVE AT SAID STRATUM TO FRACTURE THE STRATUM; AND ALLOWING THE SILICA GEL, THROUGH ITS AFFINITY WITH THE CRUDE OIL, TO BE FLOWED OUT OF THE FRACTURE RESULTING FROM SAID PRESSURIZING TO EXPOSED THE BRIDGED BIPHENYL TO SOLVENT ACTION OF THE OIL. 